Gohring, J. | Search bioRxiv

bioRxiv2023

TCR/CD3-based synthetic antigen receptors (TCC) convey superior antigen sensitivity combined with high fidelity of activation

Low antigen sensitivity and a gradual loss of effector functions limit the clinical applicability of chimeric antigen receptor (CAR)-modified T-cells and call for alternative antigen receptor designs for effective T-cell-based cancer immunotherapy. Here we applied advanced microscopy to demonstrate that TCR/CD3-based synthetic constructs (TCC) outperform second-generation CAR formats with regard to conveyed antigen sensitivities by up to a thousand-fold. TCC-based antigen recognition occurred without adverse non-specific signaling, which is typically observed in CAR-T-cells, and did not depend - unlike sensitized peptide/MHC detection by conventional T-cells - on CD4- or CD8- coreceptor engagement. TCC-endowed signaling properties may prove critical when targeting antigens in low abundance and aiming for a durable anti-cancer response.

immunology↗

bioRxiv2023

Monomeric agonist peptide/MHCII complexes activate T-cells in an autonomous fashion

Molecular crowding of agonist peptide/MHC class II complexes (pMHCIIs) with structurally similar, yet per se non-stimulatory endogenous pMHCIIs has been postulated to sensitize T-cells for the recognition of single antigens on the surface of dendritic cells and B-cells. When testing this premise with the use of advanced live cell microscopy, we observed pMHCIIs as monomeric, randomly distributed entities diffusing rapidly after entering the APC surface. Synaptic TCR-engagement of highly abundant endogenous pMHCIIs was low or non-existent and affected neither TCR-engagement of rare agonist pMHCII in early and advanced synapses nor agonist-induced TCR-proximal signaling. Our findings highlight the capacity of single freely diffusing agonist pMHCIIs to elicit the full T-cell response in an autonomous and peptide-specific fashion with consequences for adaptive immunity and immunotherapeutic approaches. SHORT SUMMARYPlatzer et al. revealed via highly quantitative and single molecule live cell microscopy the nature of peptide-loaded MHC class II molecules (pMHCII) as monomeric, densely populating, randomly distributed and predominantly rapidly diffusing entities on the surface of B-cells and dendritic cells. Low abundant stimulatory agonist pMHCII acted as autonomous units with the highest chance of T-cell detection when equally spread on APCs. The presence of bystander-pMHCII previously termed "co-agonist pMHC" affected neither synaptic agonist -TCR-binding nor efficiencies of T-cell recognition. "Co-agonist"-TCR-binding resembled random molecular collisions. Findings inform the design of T-cell-based immunotherapies.

immunology↗